Beetles, like many other insects, are commonly observed congregating around artificial light sources at night. This widespread phenomenon often leads to large numbers of these insects swarming porch lights or windows. This behavior is broadly described as positive phototaxis, indicating a natural tendency to move toward light.
The Science Behind Light Attraction
Many beetles, particularly those active at night, rely on natural light sources such as the moon or stars for navigation. This method, known as transverse orientation, involves maintaining a fixed angle relative to a distant light source, allowing them to fly in a straight line. When these insects encounter artificial lights, which are much closer, the angle to the light source changes rapidly. Their instinct to correct this angle by continuously turning results in a disoriented spiral flight path, drawing them closer to the light.
Recent research suggests insects demonstrate a “dorsal light response.” This innate behavior causes insects to orient their back, or dorsal side, towards the brightest light source, which naturally helps them maintain stable flight. However, artificial lights disrupt this natural response. The constant reorientation towards a nearby artificial light source can lead to erratic flight patterns, including continuous circling, stalling, or even inverting and crashing.
Not All Light, Not All Beetles
The attraction to light is not a universal characteristic across all beetle species or all types of light. Nocturnal beetles, those active during the night, are generally more affected by artificial lights and show higher activity compared to diurnal species. This difference stems from their reliance on ambient light for natural behaviors. Many insects, including various beetle species, are especially sensitive to specific wavelengths of light, particularly ultraviolet (UV) and blue light.
Wavelengths in the UV range (300-420 nanometers) are particularly alluring to many insects. Artificial light sources, such as cool white LEDs with higher color temperatures (above 4000 Kelvin), often emit more blue light, making them more attractive. In contrast, lights with longer wavelengths, like yellow, amber, or red, are less attractive. Insects do not perceive these warmer colors as effectively, which reduces their draw.
How Artificial Light Affects Beetles
The attraction of beetles to artificial light sources can lead to several negative consequences for their survival and ecological roles. Continuous circling around lights causes significant energy depletion, as insects expend considerable effort in their disoriented flight patterns. This disorientation also impairs their ability to perform natural behaviors such as foraging for food and locating mates.
Beetles that congregate around artificial lights become easy targets for predators, increasing their risk. This heightened predation can severely impact local beetle populations. Beyond immediate dangers, artificial light can disrupt the temporal patterns and life cycles of nocturnal beetles, interfering with their natural rhythms. Studies indicate that a substantial percentage of insects approaching artificial lights, ranging from 30% to 40%, may die due to crashes, predation, or physiological stress.
Reducing Beetle Attraction to Your Lights
To minimize beetle attraction to outdoor lighting, several practical strategies can be implemented:
Switch to yellow or amber-colored bulbs, or LED lights with warmer color temperatures (typically between 2,000 and 2,700 Kelvin), as they emit less UV and blue light.
Reduce unnecessary outdoor lighting, particularly during periods of high beetle activity, to significantly decrease their presence.
Use motion sensors to ensure lights are only activated when needed, limiting the time they can attract insects.
Direct light downwards with shields and ensure the bulb itself is covered to reduce light scatter into the environment.
Position lights strategically away from entry points like doors and windows to deter beetles from entering homes.
Maintaining clean light fixtures by regularly removing dirt and grime may also contribute to reduced attraction.